Two-Dimensional NH(4)V(3)O(8) Nanoflakes as Efficient Energy Conversion and Storage Materials for the Hydrogen Evolution Reaction and Supercapacitors

[Image: see text] Herein, for the first time, we present two-dimensional (2D) NH(4)V(3)O(8) nanoflakes as an excellent material for both energy conversion of the hydrogen evolution reaction and storage of supercapacitors by a simple and fast two-step synthesis, which exhibit a completely sheet-like morphology, high crystallinity, good specific surface area, and also stability, as determined by thermogravimetric analysis. The 2D-NH(4)V(3)O(8) flakes show an acceptable hydrogen evolution performance in 0.5 M H(2)SO(4) on a glassy carbon electrode (GCE) coated with 2D-NH(4)V(3)O(8), which results in a low overpotential of 314 mV at −10 mA cm(–2) with an excellent Tafel slope as low as 90 mV dec(–1). So far, with the main focus on energy storage, 2D-NH(4)V(3)O(8) nanoflakes were found to be ideal for supercapacitor electrodes. The NH(4)V(3)O(8) working electrode in 1 M Na(2)SO(4) shows an excellent electrochemical capability of 274 F g(–1) at 0.5 A g(–1) for a maximum energy density of 38 W h kg(–1) at a power density as high as 250 W kg(–1). Moreover, the crystal structure of 2D-NH(4)V(3)O(8) is demonstrated by density functional theory (DFT) computational simulation using three functionals, GGA, GGA + U, and HSE06. The simple preparation, low cost, and abundance of the NH(4)V(3)O(8) material provide a promising candidate for not only energy conversion but also energy-storage applications.